Many commercial products are available for treatment of dry, rough skin. The active ingredients in these products include humectants, emollients, keratolytics and occlusives. Urea, salicylic acid and white petrolatum are all known as ingredients in commercially available topical products. Urea is used in topical compositions as an emollient, humectant as well as a keratolytic. Because urea is naturally present in the stratum corneum, it is considered a natural moisturizing factor. Salicylic acid possesses keratolytic activity. White petrolatum is a hydrocarbon base that is used in ointments; it also has the additional value of being an emollient and an occlusive.
Despite their widespread use, there are significant problems with skin products that contain urea and salicylic acid. Urea is not stable in an aqueous environment, and breaks down into carbon dioxide and ammonia, with the concomitant formation of an unpleasant smell. In contrast, urea is stable in non-aqueous bases, such as hydrocarbons. However, non-aqueous bases are hydrophobic and uncomfortable to the touch, i.e. feel sticky. Additionally, these non-aqueous bases do not wash off the skin easily. The physical unpleasantness of these bases decreases patient compliance and the effectiveness of compositions that contain urea. Moreover, the salicylic acid particles are known to crystallize and localize during the shelf life of commercially available products. The non-uniformity of the salicylic acid crystals necessitated an additional step of remixing the product in order to maintain a uniform product during the shelf life of the product.
We have discovered a process to create a stable, uniform composition, with no crystal growth, comprising urea and salicylic acid in a white petrolatum base.